docs: def Harms(x, rhol, rhog, mul, mug, m, D):
      r'''Calculates void fraction in two-phase flow according to the model of 
      [1]_ also given in [2]_ and [3]_.
  
      .. math::
          \alpha = \left[1 - 10.06Re_l^{-0.875}(1.74 + 0.104Re_l^{0.5})^2
          \left(1.376 + \frac{7.242}{X_{tt}^{1.655}}\right)^{-0.5}\right]^2
          
      .. math::
          Re_l = \frac{G_{tp}(1-x)D}{\mu_l}
  
      Parameters
      ----------
      x : float
          Quality at the specific tube interval []
      rhol : float
          Density of the liquid [kg/m^3]
      rhog : float
          Density of the gas [kg/m^3]
      mul : float
          Viscosity of liquid [Pa*s]
      mug : float
          Viscosity of gas [Pa*s]
      m : float
          Mass flow rate of both phases, [kg/s]
      D : float
          Diameter of the channel, [m]
  
      Returns
      -------
      alpha : float
          Void fraction (area of gas / total area of channel), [-]
  
      Notes
      -----
      [1]_ has been reviewed.
          
      Examples
      --------
      >>> Harms(.4, 800, 2.5, 1E-3, 1E-5, m=1, D=0.3)
      0.9653289762907554
  
      References
      ----------
      .. [1] Tandon, T. N., H. K. Varma, and C. P. Gupta. "A Void Fraction Model 
         for Annular Two-Phase Flow." International Journal of Heat and Mass 
         Transfer 28, no. 1 (January 1, 1985): 191-198. 
         doi:10.1016/0017-9310(85)90021-3.
      .. [2] Xu, Yu, and Xiande Fang. "Correlations of Void Fraction for Two-
         Phase Refrigerant Flow in Pipes." Applied Thermal Engineering 64, no. 
         1-2 (March 2014): 242–51. doi:10.1016/j.applthermaleng.2013.12.032. 
      .. [3] Dalkilic, A. S., S. Laohalertdecha, and S. Wongwises. "Effect of 
         Void Fraction Models on the Two-Phase Friction Factor of R134a during 
         Condensation in Vertical Downward Flow in a Smooth Tube." International 
         Communications in Heat and Mass Transfer 35, no. 8 (October 2008): 
         921-27. doi:10.1016/j.icheatmasstransfer.2008.04.001.
      '''
      G = m/(pi/4*D**2)
      Rel = G*D*(1-x)/mul
      Xtt = Lockhart_Martinelli_Xtt(x, rhol, rhog, mul, mug)
      return (1 - 10.06*Rel**-0.875*(1.74 + 0.104*Rel**0.5)**2
              *(1.376 + 7.242/Xtt**1.655)**-0.5)